Auditory scene analysis, the ability to parse and organize the mixture of incoming sounds to coherent streams of information, is a fundamental process of the auditory system that allows us to follow a single voice in the midst of a crowded room or to listen to the melody of the flute within an orchestral suite. Accurate speech perception relies on the ability to discriminate and segregate sound elements in the acoustic signal. Despite the importance of this process for human behavior, the neural mechanisms that subserve the organization of the auditory input are poorly understood. The long term goal of the project is to understand how the human brain organizes acoustic input into meaningful auditory objects. The experiments proposed are aimed at evaluating the processing stages between sensory input and behavioral response by specifying the relationship between the stimulus-driven and attentive mechanisms that give rise to the perception of a coherent auditory environment. This will be accomplished using high temporal resolution of event-related potentials (ERPs) in conjunction with behavioral methods to compare the outcome of stimulus-driven auditory processes with the perception resulting from attentive processing of the same sounds across various experimental conditions. The results of the proposed experiments will provide new insights into the processes involved in perceiving complex auditory scenes and lead to a greater understanding of the contribution of automatic and attentional mechanisms underlying both normal and impaired auditory perception. Deficits in central auditory processing are thought to play a key role in many cognitive disorders (e.g., autism, dyslexia). Using electrophysiological measures, in conjunction with behavioral methods to understand how stimulus-driven processes and attention interact in perception will advance our understanding of impaired processing, which is essential for developing diagnostic strategies and rehabilitative treatments. Since subject response is not needed for obtaining certain ERPs, this methodological approach is advantageous for use with children and impaired populations for whom task requirements may be difficult, and thus has the potential to be an important non-invasive tool for diagnosis and assessment of central auditory processing deficits.